This invention relates to the production of synthetic diamond films. More particularly, the present invention relates to diamond coated laminates suitable for visible and infrared optical devices, and methods for production of diamond films and diamond coated laminates.
Chemical vapor deposition of diamond films onto substrates is known. Such diamond coatings typically nucleate at discrete sites, forming crystalline particles that merge into a film when the sizes of the growing particles exceed the particle spacing. The growth surfaces of such films possess a large surface roughness that scatters optical radiation and thus lowers the optical transparency of the film.
The art has attempted to overcome this disadvantage of diamond films by substrate pretreatment in which a diamond paste or diamond powder is used to polish the substrate, which is then cleaned prior to deposition of the diamond film. Such pretreatment is effective to increase the nucleation density of the deposited film, and thus reduce overall surface roughness and improve transparency. However, such substrate surface pretreatment methods are labor intensive, time consuming and costly.
Methods for nucleating films of diamond microcrystallites which produce smoother and thus more transparent diamond films have been reported. However, these methods are limited to films having a thickness of less than 3 millionths of a meter.
U.S. Pat. No. 4,939,763 to Pinneo et al discloses a method for making synthetic diamond films which are transmissive to X-ray radiation in which diamond is deposited upon a substrate to a preselected thickness, selected areas of the opposite surface of the substrate are masked, and the unmasked areas are removed by etching to expose the diamond film. Alternatively, the entire substrate may be etched away.
U.S. Pat. No. 4,907,846 to Tustison et al discloses thick, impact resistant antireflection coatings for infrared transparent optical elements such as zinc selenide and zinc sulfide comprising an impact protection material having a relatively high modulus of elasticity compared to the modulus of elasticity of the optical element material. An antireflection layer is deposited over the impact protection layer. Hard carbon, diamond, cerium oxide, titanium oxide, zirconium oxide, and mixtures thereof may be used as the impact protection layer if a yttrium oxide adhesion layer is interposed between the optical element and the impact protection layer. Differences in optical matching between the antireflection layer and the IR transparent substrate are compensated by adjusting the thickness of the antireflection layer to a quarter wavelength of the wavelength which is desired to be maximally transmitted through the optical element.
U.S. Pat. No. 4,915,977 to Okamoto et al discloses an improved method of forming a diamond film on a substrate in which a first gas selected from the group consisting of hydrogen, inert gases, organic compound gases and mixtures thereof is introduced into a vacuum vessel to contact a substrate housed therein, and carbon is evaporated onto the substrate by arc discharge at a carbon cathode while a negative voltage is applied to the substrate or substrate holder, to form a diamond film on the substrate.
U.S. Pat. No. 4,939,043 to Biricik et al discloses an infrared transparent, electrically conductive semiconductor window comprising a substrate of zinc selenide or zinc sulfide and a thin coating of doped semiconductor material selected from the group consisting of gallium arsenide, gallium aluminum arsenide, semiconducting diamond, zinc selenide, zinc oxide, zinc sulfide, silicon, germanium, and semiconducting silicon carbide.
One object of the present invention is to provide a relatively economical and rapid method for the production of a transparent diamond film suitable for use in an optical device.
Another object is to provide a method for production of a transparent diamond film having a thickness greater than 3 millionths of a meter.
A further object is to provide a method for production of a diamond film having two smooth surfaces, which is suitable for use in an optical device.